Abstract

The crystallization of lithium hydroxide by a membrane crystallization process was studied, assessing different operational conditions, such as the temperature of the feed Li brine, the flow rate, and the water activity of the permeate, to determine the effect of these variables on the crystallization process. Results showed good agreement with classical crystallization theory, where larger crystal sizes were obtained for lower supersaturation conditions, such as when operating at 40 degrees C, a flow rate of 0.6 L/min, and a water activity of 1.0. The mentioned conditions resulted in a lower starting flux, and compared to tests that promote a maximum flux, there is a difference of 58 % between the lowest and highest values. However, crystal size impacted the formation of crystals on the membrane surface, reducing the transmembrane water flux drastically, even reaching similar flux values of approximately 1 kg/m2h between all conditions. The induction times indicated that the supersaturation condition values required to start the crystal nucleation ranged between 1.08 and 1.20 for all conditions assessed. The analysis of the membrane surface at the end of each test demonstrated that smaller crystal sizes caused a more detrimental impact on the crystal layer formed in terms of the membrane area blocked. Therefore, lower supersaturation conditions that promote the formation of larger crystals are suggested for the further development of the process, in the perspective of industrial applications, to avoid detrimental fouling formation on the membrane. Besides, the similar water flux values reached in the crystallization step for all operational conditions confirm that a similar membrane area will be required to achieve certain productivity. Hence, the results are promising for defining the best operating conditions of the process with a view to future industrial applications.